Wireless Local Area Networks (WLANs) have become the focus of intense research efforts owing to the user's growing necessity to have greater connectivity to a myriad of wired and wireless networks, and hence greater mobility. Wireless networking products such as personal computers (PCs), laptops and other portable devices incorporate a Network Interface Card (NIC), which provides connection via a wireless medium to other such devices.
IEEE 802.11 is a standard, hereinafter referred to as “802.11”, developed by the Institute of Electronic and Electrical Engineers (IEEE) for operation of wireless LAN devices currently covered within the 2.4 GHz and 5 GHz bands but, which can be extendable to other bands. The most common architecture of an 802.11 LAN is a group of stations (STAs) or clients, for example a group of PCs and/or laptops, and an Access Point (AP) that provides access to other networks, such as wired networks, by controlling connection of stations to the LAN. The AP also provides data forwarding services for the stations: frames are not passed directly between stations but always go via the AP. This is known as an infrastructure mode. An alternative wireless architecture where the LAN does not include an AP is called an Independent Basic Service Set (IBSS).
A wireless network enables the transfer of information from one device to another by the implementation of several functions including: a medium which provides a data transmission path; Medium Access Control (MAC) protocol to define how stations share a common medium; synchronisation and error control protocols to ensure that data transfer within each link in the network is intact; encryption services for secure data transmission; mechanisms for transferring the data from the source to the recipient; and connectivity software for interfacing an appliance to application software on a server.
FIG. 1 shows the logical architecture of the 802.11 standard that applies to each station. The fundamental purpose of the MAC layer 10 is to provide access control functions for shared medium Physical Layers (PHYs) 20 in support of the LLC (logical link control) layer 30, with Network and Upper layers 40 above the LLC layer.
Before transmitting a frame, the MAC co-ordination of an 802.11 wireless LAN takes measures to avoid collisions by using one of two protocols, for example, carrier sense multiple access/collision avoidance (CSMA/CA). Within the 802.11 standard this mode is specified as the Distributed Coordination Function (DCF), which is a contention-based protocol. Another mode is the priority-based Point Coordination Function (PCF) which is a contention-free access protocol for infrastructure mode configurations.
The 802.11 standard outlines the media access control (MAC) and the physical layer (PHY) layer specifications for wireless LANs. 802.11 utilises three transmission technologies including Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS). Moreover, the DSSS system of the 802.11 standard operates at data rates of 1 Mbps and 2 Mbps only. Products conforming strictly to the 802.11 standard operate in the 2.4 GHz ISM band between 2.4000 and 2.4835 GHz.
With subsequent developments in the technology, the DSSS wireless LANs could exchange data at up to 11 Mbps, a consequence of which was that devices had problems with interoperability and implementation under 802.11.
More specifically, the IEEE802.11b standard, hereinafter referred to as ‘802.11b’, emerged from 802.11 as the “high rate” and Wi-Fi™ standard specifying the DSSS system to operate at 1, 2, 5.5 and 11 Mbps. The 802.11b compliant devices operate in only the 2.4000 GHz ISM band between 2.4000 and 2.4835 GHz. The IEEE 802.11a standard, hereinafter referred to as ‘802.11a’, for device operability at the higher 54 Mbs rate in the 5 GHz band, can support even higher data rates owing to the implementation of Orthogonal Frequency Division Modulation (OFDM).
Consequently, two major variants have emerged from the IEE802.11 specifications, namely the 802.11b and 802.11a standards. The 802.11b standard operating on the 2.4 GHz band is the most prevalent but is limited to a peak data rate of 11 Mbps available on a limited number of channels, while the higher data rate 802.11a network operating on the broader 5 GHz band has a greater number of channels than 802.11b. The new 802.11a standard offers a higher peak data rate of 54 Mb/s by implementing OFDM.
Hitherto, most products have been 802.11b-compliant and therefore use the 2.4 GHz band, and currently there are few 802.11a-compliant products on the enhanced 5 GHz band. Hence the principal problem in this context facing the information technologist is that network administrators who have a large network of existing 802.11b users will not all be able to upgrade from 802.11b to 802.11a simultaneously in order to exploit the higher data rates available on the latter. The feasibility of the upgrade poses a considerable burden to network administrators as upgrading all stations from 802.11b to 802.11a is not economical and/or practical.
Most recently, yet a further variant on the IEE 802.11 specification has been proposed, the 802.11g standard. This employs the same band as the 802.11b standard, but is, in certain modes, incompatible with it. It is conceivable that further non-interoperable and/or interfering standards may be developed in the future. This will increase still further the difficulty of integration.
The current invention provided for a solution to the problems of the prior art.